1. Field of the Invention
This invention relates to wireless communication systems, and more particularly to a method and apparatus for efficiently allocating bandwidth between base stations and customer premises equipment in a broadband wireless communication system.
2. Description of Related Art
As described in U.S. Pat. No. 6,016,311, by Gilbert et al., issued Jan. 18, 2000, entitled “Adaptive Time Division Duplexing Method and Apparatus for Dynamic Bandwidth Allocation within a Wireless Communication System,” hereby incorporated by reference, a wireless communication system facilitates two-way communication between a plurality of subscriber radio stations or wireless subscriber radio units (fixed and portable) and a fixed network infrastructure. Exemplary communication systems include mobile cellular telephone systems, personal communication systems (PCS), and cordless telephones. The key objective of these wireless communication systems is to provide communication channels on demand between the plurality of wireless subscriber radio units and their respective base stations in order to connect a wireless subscriber radio unit user with the fixed network infrastructure (usually a wire-line system). In the wireless systems having multiple access schemes a time “frame” is used as the basic information transmission unit. Each frame is sub-divided into a plurality of time slots. Some time slots are used for control purposes and some for information transfer. Wireless subscriber radio units typically communicate with the base station using a “duplexing” scheme thus allowing the exchange of information in both directions of connection.
Transmissions from the base station to the wireless subscriber radio unit are commonly referred to as “downlink” transmissions. Transmissions from the wireless subscriber radio unit to the base station are commonly referred to as “uplink” transmissions. Depending upon the design criteria of a given system, the prior art wireless communication systems have typically used either time division duplexing (TDD) or frequency division duplexing (FDD) methods to facilitate the exchange of information between the base station and the wireless subscriber radio units. Both the TDD and FDD duplexing schemes are well known in the art.
Recently, wideband or “broadband” wireless communications networks have been proposed for providing delivery of enhanced broadband services such as voice, data and video services. The broadband wireless communication system facilitates two-way communication between a plurality of base stations and a plurality of fixed subscriber stations or Customer Premises Equipment (CPE). One exemplary broadband wireless communication system is described in the co-pending application and is shown in the block diagram of FIG. 1. As shown in FIG. 1, the exemplary broadband wireless communication system 100 includes a plurality of cells 102. Each cell 102 contains an associated cell site 104 that primarily includes a base station 106 and an active antenna array 108. Each cell 102 provides wireless connectivity between the cell's base station 106 and a plurality of customer premises equipment (CPE) 110 positioned at fixed customer sites 112 throughout the coverage area of the cell 102. The users of the system 100 may include both residential and business customers. Consequently, the users of the system have different and varying usage and bandwidth requirement needs. Each cell may service several hundred or more residential and business CPEs.
The broadband wireless communication system 100 of FIG. 1 provides true “bandwidth-on-demand” to the plurality of CPEs 110. CPEs 110 request bandwidth allocations from their respective base stations 106 based upon the type and quality of services requested by the customers served by the CPEs. Different broadband services have different bandwidth and latency requirements. The type and quality of services available to the customers are variable and selectable. The amount of bandwidth dedicated to a given service is determined by the information rate and the quality of service required by that service (and also taking into account bandwidth availability and other system parameters). For example, T1-type continuous data services typically require a great deal of bandwidth having well-controlled delivery latency. Until terminated, these services require constant bandwidth allocation on each frame. In contrast, certain types of data services such as Internet protocol data services (TCP/IP) are bursty, often idle (which at any one instant requires zero bandwidth), and are relatively insensitive to delay variations when active.
Due to the wide variety of CPE service requirements, and due to the large number of CPEs serviced by any one base station, the bandwidth allocation process in a broadband wireless communication system such as that shown in FIG. 1 can become burdensome and complex. This is especially true with regard to the allocation of uplink bandwidth. Base stations do not have a priori information regarding the bandwidth or quality of services that a selected CPE will require at any given time. Consequently, requests for changes to the uplink bandwidth allocation are necessarily frequent and varying. Due to this volatility in the uplink bandwidth requirements, the many CPEs serviced by a selected base station will need to frequently initiate bandwidth allocation requests. If uncontrolled, the bandwidth allocation requests will detrimentally affect system performance. If left unchecked, the bandwidth required to accommodate CPE bandwidth allocation requests will become disproportionately high in comparison with the bandwidth allocated for the transmission of substantive traffic data. Thus, the communication system bandwidth available to provide broadband services will be disadvantageously reduced.
Therefore, a need exists for a method and apparatus that can dynamically and efficiently allocate bandwidth in a broadband wireless communication system. The method and apparatus should be responsive to the needs of a particular communication link. The bandwidth needs may vary due to several factors, including the type of service provided over the link and the user type. The bandwidth allocation method and apparatus should be efficient in terms of the amount of system bandwidth consumed by the actual bandwidth request and allocation process. That is, the plurality of bandwidth requests generated by the CPE should consume a minimum percentage of available uplink bandwidth. In addition, the bandwidth allocation method and apparatus should respond to bandwidth requests in a timely manner. Bandwidth should be allocated to high priority services in a sufficiently short time frame to maintain the quality of service specified by the CPE. Further, the bandwidth allocation method and apparatus should be capable of processing an arbitrarily large number of bandwidth allocation requests from a relatively large number of CPEs. For example, in the system shown in FIG. 1, as many as one hundred CPEs may be allowed to be simultaneously active, coordinating their transmissions on the uplink. Furthermore, the system can accommodate approximately one thousand CPEs on the physical channel. Therefore, the need exists for a bandwidth allocation method and apparatus that can process and respond to the bandwidth allocation requests generated by a large number of CPEs.
Some prior art systems have attempted to solve bandwidth allocation requirements in a system having a shared system resource by maintaining logical queues associated with the various data sources requiring access to the shared system resource. Such a prior art system is taught by Karol et al., in U.S. Pat. No. 5,675,573, that issued on Oct. 7, 1997. More specifically, Karol et al. teach a bandwidth allocation system that allows packets or cells within traffic flows from different sources that are contending for access to a shared processing fabric to get access to that fabric in an order that is determined primarily on individual guaranteed bandwidth requirements associated with each traffic flow. In addition, the system taught by Karol et al. allow the different sources to gain access to the shared processing fabric in an order determined secondarily on overall system criteria, such as a time of arrival, or due date of packets or cells within the traffic flows. Packets or cells of data from each data source (such as a bandwidth requesting device) are queued in separate logical buffers while they await access to the processing fabric.
A need exits for a bandwidth allocation method and apparatus for efficiently processing and responding to bandwidth allocation requests. The bandwidth allocation method and apparatus should accommodate an arbitrarily large number of CPEs generating frequent and varying bandwidth allocation requests on the uplink of a wireless communication system. Such a bandwidth allocation method and apparatus should be efficient in terms of the amount of bandwidth consumed by the bandwidth request control messages exchanged between the plurality of base stations and the plurality of CPEs. In addition, the bandwidth allocation method and apparatus should respond to the bandwidth allocation requests in a timely and accurate manner. The bandwidth allocation method and apparatus should also be able to process an arbitrarily large number of bandwidth allocation requests generated by a relatively large number of CPEs. The present invention provides such a bandwidth allocation method and apparatus.